The invention concerns a method for assembling in a fluidtight manner, by soldering, a header plate delimiting a heat exchange fluid box and a multiplicity of parallel elongate tubes whose ends pass through respective holes in the said header plate to allow communication of fluid between the inside of the tubes and the inside of the fluid box, a method in which a solder is made to melt in order to provide a fluidtight connection between the periphery of each hole and the external surface of the corresponding tube.
Such a method is used in particular for assembling a heat exchanger intended for the exchange of heat between the exhaust gases of a vehicle, circulating outside the tubes, and a cooling fluid circulating inside the tubes, an exchange of heat which makes it possible to use some of the heat energy from the exhaust gases for heating the passenger compartment of the vehicle.
In this type of exchanger, in order to resist the corrosive nature of the exhaust gases, the parts are made from stainless steel and the solder is based on nickel.
Various techniques are used for applying this solder. One of them consists of depositing drops of solder in a viscous state on the header plate with a syringe, after fitting the tubes and close to these. Other techniques consist of soaking the ends of the tubes, assembled in a bundle, in a liquid containing the solder, or spraying the solder with a gun in the powder state on the ends of the tubes in the bundle, or on the header plate before fitting the tubs. All these techniques require manipulations which are complex and sometimes tricky and do not allow good control of the quantity of solder applied or a good seal between the tubes and the header plate.
The aim of the invention is to remedy these drawbacks.
The invention relates notably to a method of the type defined in the introduction, and provides for the solder to be applied to at least one of the faces of the header plate, before insertion of the ends of the tubes, in the form of a flexible adhesive sheet previously perforated in correspondence with the holes in the plate.
Such adhesive sheets of solder, notably based on nickel, are currently commercial available, for example in the form of strips provided with protective films, and are used for assembling parts having continuous respective surfaces which are applied against each other with the interposing of the sheet of solder.
Other optional characteristics of the invention, complementary or alternative, are set out below:
The contour of the perforations of the sheet of solder coincides substantially with that of the holes in the header plate.
The perforations in the sheet of solder are smaller than the holes in the header plate.
The perforations in the sheet of solder have substantially the same shape and the same centre as the holes in the header plate.
The contour of a perforation in the sheet of solder has common points with that of the corresponding hole in the header plate, and is for the remainder situated inside the contour of the hole.
The contour of the perforation moves progressively away from that of the hole as from the common point.
The contour of the perforation moves away abruptly, by means of a step, from that of the hole as from a common point.
The contour of the perforation, between two steps, remains at a substantially constant distance inside that of the hole.
With each perforation in the sheet of solder there is associated a collar formed by conjoint cropping and deformation of the sheet and extending substantially in the longitudinal direction of the tube as from the said sheet.
The starting point is a sheet of solder having an adhesive face and provided with a protective film at least on the said adhesive face, and the sheet is cropped in order to adapt it to the shape of the header plate and to produce the perforations, before removing the protective film and applying the sheet to the header plate.
The sheet is provided with a second protective film opposite to the said adhesive face, which is removed after application of the sheet and before melting of the solder.
The tubes are fitted by causing them to pass through the holes in the said header plate covered by the sheet.
The solder is based on nickel.
The header plate and the tubes are made from stainless steel.